World number one Rafael Nadal remained on course to retain his Madrid Masters title with a comfortable 6-1, 6-4 win over Finland's Jarkko Nieminen on Thursday.
Next up for the 13-time Grand Slam champion is a meeting with sixth seed Tomas Berdych after the Czech came through in three sets against Bulgarian 12th seed Grigor Dimitrov 3-6, 6-3, 6-2.
Japan's Kei Nishikori continued his fine form on clay after winning in Barcelona two weeks ago as he outlasted eighth seed Milos Raonic in two tie-breaks 7-6 (7/5), 7-6 (7/5).
Serena Williams maintained her quest for a third consecutive Madrid Open title with a 6-2, 6-3 win over Spain's Carla Suarez Navarro.
Maria Sharapova also moved into the last eight with a 6-4, 6-3 win over Australian Samantha Stosur and set up an intriguing quarterfinal against world number two Li Na, who came from a set down to beat 16th seed Sloane Stephens 2-6, 6-3, 6-2 to reach last eight.